Re-set means for acceleration integrator



Aug 30, 1960 P. J. RAINSBERGER ETAL 2,950,908

REI-SET MEANS FOR ACCELERATION INTEGRATOR Filed June 27, 1958 INVENTOR.fa UZ rZ-a'a'z S eye?- 115 5907?@ Z627 T Z218' C@ 7.

United States Patent() RE-SET MEANS FOR ACCELERATION INTEGRATOR FiledJune 27, 1958, Ser. No. 745,169 4 Claims. (Cl. 73-503) Paul J.Rainsberger, Fischer, Phoenix, trols Corporation,

This invention relates to acceleration integrators which utilize, as ameasure of the time integral of acceleration, the movement of a pistonin a cylinder in which it is substantially free to move except for theopposition of a partially confined fluid medium.

More particularly, the invention provides improved holding and re-setmeans for returning the piston of such an acceleration integrator to itsrest position following a cycle of operation, and for holding the pistonreliably in that position until released in response to an appliedacceleration. In previous acceleration integrators of the describedtype, that holding and re-set function is performed by a spring whichcontinuously urges the piston vtoward its rest position, and whichtherefore opposes the piston movement in response to acceleration. Theaction of such a spring during operation of an acceleration integratortends to produce non-linearity of the response.

The present invention avoids such inaccuracies, which were inherent inmany prior art devices, by providing a remarkably simple and reliableholding and re-set mechanism which completely releases the piston duringnormal operation of the device. That release is effected directly andautomatically in response to an applied acceleration that exceeds apredetermined threshold value. The operation and advantages of theinvention will be best understood in relation 4to the followingdescription of an illustrative embodiment thereof, in connection withthe attached drawings, in which:

Fig. l is a schematic axial section representing a prior artacceleration integrator during operation;

Fig. 2 is an axial section representing an illustrative embodiment ofthe invention in rest position; and

Fig. 3 is a section corresponding ot Fig. 2, but representing the deviceduring operation.

It will be helpful to discuss the operation of a typical prior artdevice in order to illustrate the operation and advantages of theinvention. Referring to Fig. 1, a fluid, typically comprising an inertgas, is confined within the sealed container 10. A cylinder assembly 11is mounted within the sealed container, the assembly comprising acylinder wall 12, a closed end wall 14, and an open end wall 20. Afreely movable piston 22 slidingly engages the inside wall of thecylinder between the two ends. A chamber 15 of variable size is thusformed within cylinder 12 between piston 22 and end wall 14. Arestricted orifice 16 in end wall 14 permits limited fluid flow betweenthat chamber and the surrounding space within container 10. The pistonis yieldingly urgedv toward the open wall 20 by a tension spring 26, andis normally held in a definite rest position defined by wall 20 when thedevice is not subject to an acceleration. When the device is acceleratedbodily toward the end 20, that is, toward the left as shown, asindicated by the arrow A in Fig. 1, piston 22 tends to move in theopposite direction toward end 14, pressurizing the fluid in the chamberand forcing it through orifice 16 at a limited rate which increases withthe magnitude of the A 62 is bored at 2,950,908 Patented Aug. 30, 1960acceleration. The fluid leaving orifice 16 travels around the outside ofthe cylinder walls, as indicated by the light arrows, and enters thecylinder behind the piston through an opening 21 in open end 20. Whensubstantially all of the fluid has been forced through the orifice, theelectrical contacts 18 and 24 close and complete a circuit between twoexternal terminals on the container 10, which are not shown in theschematic illustration.

Assuming that piston 22 is always returned to the same rest positionbefore acceleration is applied tothe device, the time required for thecontacts 24 and 18 to close after an acceleration is applied will`depend on the amount of time required to force substantially all of theconfined fluid through the orifice. Since the magnitude of the pressuredifferential across the orifice depends on the magnitude of the appliedacceleration, the contacts will thus close for some relatively fixedvalue of the integral of acceleration with respect to time. Theparticular integral value is determined in part by the amount ofobstruction offered by the orifice, which in practice may be adjustable.

In order for the device to be accurate it is necessary that the piston22 always start from the same position when an acceleration is appliedto the device. For this reason, spring means 26 are ordinarily attachedbetween the piston and the end 20 of the cylinder to restore the pistonto a uniform rest position and to hold it there until an acceleration isapplied to the device. In practice the spring 26 usually must be strongenough to support the weight of the piston and to overcome the staticfriction of the piston. In addition, the spring must be strong enough tohold the piston 22 securely in its rest position against end wall 20under the influence of normal vibration and jolts. Ordinarily a springis used which exerts a force equivalent to at least from 1.5 to 2 timesthe weight of the piston.

A serious disadvantage of such prior art devices is the fact that thespring force acts not only prior to the application of acceleration, butalso during such acceleration. Hence, the force exerted by the pistonupon the fluid in chamber 15 is not accurately proportional to the valueof the acceleration, but rather to the difference between thataccelerationand a substantially fixed quantity due to the spring action.If the device is to be employed for integrating'only accelerationshaving substantially a fixed value, that effect of the re-set spring canbe fully compensated by suitable calibration of the device. But whenemployed to integrate variable accelerations, the spring action tends toproduce an undesirable non-linearity of response. An important object ofthe present invention is to provide a means for dependably returning thepiston to its rest position and holding it there against the force ofgravity and normal vibration without the non-linearity of responseinherent in previous re-set means of the type described.

Fig. 2 shows a section of an acceleration integrator utilizing oneembodiment of the invention. A cylindrical container 28 with ahermetically sealed end cover 68 is filled with a suitable fluid, whichwill be considered for definiteness to comprise a gas such as nitrogen,for example. A cylinder assembly 30 is mounted within the containerbetween the cover 68 of the container and a spacer 36 at the bottom ofthe container. The cylinder assembly comprises a cylindrical wallportion 32 and two end portions 34 and 56. The piston 38 is slidableaxially within cylindrical wall 32, forming with that wall and end wall56 a closed chamber 39. End portion 56 is provided with a restrictiveorifice, shown as a coaxial bore 57 counterbored at its outer end toreceive the valve-forming needle 60. Valve needle 60 is coaxiallythreaded in a mounting plate 62. Plate 64 to allow unobstructed passageof gas.

therethrough. A cap 66 of electrically insulative material fits over theend portion 56 of the cylinder assembly and positions it in container28. Cap 66 has a coaxial bore 67V and is radially .channeled at69 toper-V mit unobstructed passagegof gas from `valve 66 to the annularchamber 'tjoutside of the cylinder structure. Channels 69 alsopermitpassage of the electrical conductors 46 and 74, which communicatewith the insulated terminals 70 and 72 in cover 68 of the container.Cover 68 has an axial opening 65 which provides access to the adjustmentfor needle 6l?, and also provid-es access for filling the container withgas. This opening is then hermetically sealed by a seal 75. Terminals.70 and 72 lare also hermetcallysealed. The other end 34 of the cylinderhas an opening 73 in its central portion which communicates with radialchannels 36a in spacer An electrical-switch contact 42 is mounted on theinner' face of the piston and is connected to terminal 70 by theflexible pigtail 4e and conductor 46. Pigtail 44 is highly flexible andexerts only negligible force onv the piston. A second electrical switchcontact 58 is fixedly mounted on cylinder end 56 in opposing alignmentwith contact 42.. Contact is connected through member 56, which is madeof conducting material, and conductor 74 to terminal 72. Movement ofpiston 38 to the right on the drawing closes contacts 42 and 56,oompleting a circuit between terminals 70 and 72 on the end `of thecontainer. That circuit may be utilized in known manner to perform anydesired indicating or control function.

Additional indicating means may be provided. For example, a fixed switchcontact 52 and a spring-supported contact 54 are represented as mountedon end piece 34 in position to be closed in response to movement of thepiston in its extreme left, or rest position. When the piston moves awayfrom its rest position spring 54 moves away from contact 52, producingan electrical signal.

The leads and terminals `for this switch are not shown explicitly in thedrawing, but may be similar to those already described.

The structure, as so far described, is functionally similar to the priorart device illustrated in Fig. l, except for the absence of the tensionspring 26. The functions performed by the spring 26 in the device ofFig. 1 are performed by the re-set structure now to be described. Anlannular re-set mass 76 is adapted to slide axially within the annularrecess 77 formed in the inner face of the cylinder end 56. A compressionspring 80 acts between the bottom of recess 77 andthe peripheral ange 81formed at the left end of the annular mass. A spacer 78 of resilientmaterial is preferably mounted on Vthe left end of mass 76facing piston38.

When the device is at rest or when the axial acceleration is below apredetermined threshold value, spring 80. presses mass 76 against theend of the piston 38, causing the latter toV abut against cylinder Vend34, as shown in Fig. 2. When an acceleration greater than thatpredetermined threshold value is applied to the device, as indicated inFig. 3 by t`ne arrow A, mass 76 compresses spring t and moves rapidlyinto recess 77, to the position Vshown in Fig. 3. At the same time,piston 38 movesk away from its rest position, but that movel ment israpidly checked by compression of the gas in` Hence the piston isreleased from the chamber 39. action of spring 8@ and `acts as a freemass. The piston therefore presses againstthe confined gas with a forcevery closely proportional to the magnitude of the acceleration A,forcing the gas through the orifice and around the outside of thecylinder, as indicated by the light arrows. When substantially all ofythe confined gas has escaped Vfrom chamber 39 through the orifice,

the"- contacts 42 and 58 close, thus providing a signaly at` a time whenthe integral of acceleration with respect to. time reaches apredetermined value, in the manner' Cil discussed in connection with theprior art device of Fig.

l. The indication obtained with the improved device, however, is moreaccurate and reliable than that of the prior art device, since allpotential non-linearity and other inaccuracies due to spring 26 areeliminated without sacrificing accuracy` in Ythe-starting position ofthe piston. y

The weight of re-set mass 76 Yand the strength of spring 80 may bevaried according to the type of service for which the device isintended. It is usually desirable that the piston be held securely inrest position against a disturbing force, which may be expressed as somemultiple of the acceleration of gravity g, and which is typically atleast about 1.5 g. For that purpose, spring 80 must exert a forcecorresponding to that multiple of g acting on both the piston and there-set mass. It is usually desirable, further, that the threashold valueof acceleration at which the piston is completely released be as closeas possible to the defined disturbing force. We have discovered thatthis can be accomplished by making the re-set mass considerably heavierthan the piston, typically from about 2 to about 5 times the weight ofthe piston. For example, if the weight of re-set mass 76 is-3 times thatof piston 38, and if the strength of spring 80 is suicient to hold thepiston securely in rest position against a disturbing forcecorresponding to an acceleration of' 1.5 g., then the thresholdacceleration at which the piston is fully released is substantially 2 g.Or, as a further example, with Ythe stated weight ratio, a spring forcecomputed to release the piston fully at accelerations exceeded athreshold Value of 5 g. will hold'the piston securely against disutrbingforces up to 4 g.

' It is also desirable that re-set mass 76 fit -as closely as possiblewithin recess 77, so that the volume of gas contained between the massand the recess walls be kept relatively small. It is desirable foraccuracy of the device that substantially all of the gas initiallycontained in chamber 39 be forced through the orifice before the switchcontacts 42 and 58 close. This condition is desirable so that theoperation of the contacts will be independent of the magnitude of theacceleration and depend only on its time integral. In this respect theannular design used in this embodiment has the advantage of minimizingthe amount of gas remaining between the piston and its opposing cylinderand at the time that the contacts close.

An additional feature of the invention resides in its adaptability foruse in calibration of the device. Acceleration integrators of thisgeneral type are ordinarily calibrated on a centrifugal table, which isbrought up to a constant speed to provide a known acceleration input tothe device.Y However, since the table must be first accelenated up toits chosen speed fthe piston must be artificially restrained frommovement in some way so that the time at which the known accelerationbecomes effective is accurately known. By forming the mass 76 wholly orpartially of a magneticrmaterial, and the walls of the cylinder andcontainer of non-magnetic material, and by placing a solenoid over theend of the container near the rest position of the piston and passing anelectric current therethrough, the piston may conveniently be held -inits rest position until the chosen value of accelerationis reached onthe accelerating table. The device may then be made to begin operationat a known time'by breaking the circuit to the solenoid. Then theproduct of the known acceleration multiplied by the time required forthe contacts to close gives an indication of the actual operationswitch, rather than by the direct influe alone upon mass 76.

nce of acceleration This may be accomplished, for example, by mounting asolenoid near the closed end of the cylinder, either within or outsideof the container, and energizing the solenoid via an accelerationsensitive switch which closes whenever the selected thresholdacceleration is exceeded. The re-set mass will then be drawn away from'the iston due to the magnetic torce of the solenoid For such operationthe piston and the cylinder walls must be non-magnetic and the re-setmass Snell use of a solenoid has certain advantages in that ther-nass ofthe member 76 may be made as small as desired by increasing the strengthof the magnetic iield. lt may therefore be desirable in some embodimentsof the invention to use the combination of a non-magnetic free pistonwith a magnetic member 76, non-magnetic walls 32, a solenoid around theend 56 of the cylinder assembly inside of the container, and anacceleration sensitive switch operable to energize the solenoid whenacceleration exceeds the threshold value.

Although this invention has been described with reference to onespecilic embodiment thereof, it should be understood that the inventionis by no means limited to that specific embodiment. Many modilicationsmay be made in the specilic structure disclosed without departing fromthe spirit of the invention. The invention includes all suchmodifications falling within the scope of the following claims.

We claim:

1. In combination with an acceleration integrator which comprisesstructure forming a cylinder closed at one end, piston means having asubstantially flat inner axial face and movable inwardly in the cylinderin response to axial acceleration thereof, gaseous uid means operable tolimit the rate of piston movement, and abutment means adjacent the opencylinder end operable to limit outward piston movement; iston re-setcomprising a re-set mass of for n normally positioned between the pistonand the closed cylinder' end, an annular recess formed in the closedcylinder en, adapted to receive the re-set mass, the outer axial face ofthe re-set mass being substantially aligned with the closed cylinder endwhen the re-set mass is received in Said recess, and the re-set mass andannular recess so corresponding in size and el tpe as to minimize thevolume of gas entrapped by inward movement of' the piston to the closedcylinder end, and compression spring means acting between the re-setmass and the bottom of said recess.

2. rhe combination deiined in claim 1, wherein the force exerted by saidspring just exceeds the combined weight or" the re-set mass and pistonmeans.

3. The combination deiined in claim 1, wherein the weight of the re-setmass is between about 2 and about 5 times the weight of the pistonmeans.

4. The combination defined in claim 1, wherein the re-set mass comprisesmagnetic material, and the piston is free of magnetic material.

References Cited in the le of this patent UNITED STATES PATENTS

